Shaft clamp assembly

ABSTRACT

A shaft clamp assembly ( 10 ) includes a bracket having a tubular member adapted to receive a shaft, for example the shaft of an umbrella, a device for mounting the tubular member ( 11 ) to a structure, for example a table, and a clamping element ( 15 ), the clamping element being operable to secure the shaft to the tubular member, and wherein the internal wall of the tubular member is provided with at least two shaft contact surfaces, their arrangement being such that a triangle of forces is generated between the clamping element and the shaft contact surfaces to secure the shaft to the tubular member when the clamping element is operated.

FIELD OF THE INVENTION

This invention relates to a shaft clamp assembly, in particular, but notexclusively to a shaft clamp assembly for securing the shaft of a sunumbrella or weather screen to a supporting structure.

BACKGROUND

Increasingly weather screens, some in the form of umbrellas, are used inoutdoor settings, for example street-side cafés, restaurant lawns,fairs, picnics and barbecues. They provide shelter from the sun or rain,and often also complement the appearance of a table setting, or evenprovide a means for displaying advertising.

Due to the large size of many of these umbrellas once opened out, theyare often difficult to hold steady in even mild wind conditions. Mostcommonly very heavy and/or large base blocks or base members are used tohold the shaft of the umbrella. Because of the temporary or collapsiblenature of umbrellas, they are items that are put up, moved around andput away regularly. These heavy or cumbersome bases are often the mostdifficult items to handle.

Sometimes umbrellas are held steady by inserting the lower end of themain shaft into the ground. This is often difficult to do, and in anycase the ground often provides a poor support for the umbrella.

In addition to heavy base blocks, or holes in the ground, some bracketdesigns have been produced which comprise a circular tube in which theshaft of an umbrella is clamped. However, the forces acting on the bodyof the umbrella are often significant, and these brackets are ofteninadequate to support an umbrella in even light wind conditions. It istoo easy for an umbrella shaft which is clamped into a circular tube topivot a little about the clamp and to move. This often results in damageor wearing of the shaft, and excessive movement of the umbrella canopy.

Often the umbrellas that are used with an item of furniture, passthrough a designated aperture in the furniture, and can gain somesupport from the furniture. However, umbrellas that are used with itemsof furniture in this way, even when heavy base blocks are used, arestill prone to a degree of instability. Umbrellas can fly right out of atable setting in a gust of wind, or blow over.

Furthermore, umbrellas used in conjunction with tables are cumbersome tomove. For example, if a street café owner wants to move a table around,he must struggle to move the table, the umbrella, and its base at thesame time, or else dis-assemble the three items and move themseparately. This process is difficult and may damage one or other of thetable, umbrella or base, and in any event it is time consuming.

Poorly secured umbrellas can also become a danger to those around them.Umbrellas lifted or pushed over by a gust of wind can be quite dangerousto those in the vicinity.

In addition, the commonly used base blocks used with umbrellas can beunsightly and intrusive in a table setting. They can severely restrictfoot-room under a table, and can make it difficult to stow chairs undera table when the table is not in use.

Another problem experienced with umbrellas and furniture is that as thesun moves, or the direction of rain changes, it is often desirable toalter the location of the umbrella relative to the item of furniture.This has been addressed to some extent by having a pivoting joint partway up an umbrella shaft, so that the canopy of the umbrella can betilted. This solution is often inadequate in providing the optimumprotection to those seated about an item of furniture.

OBJECT

It is therefore an object of the present invention to provide a shaftclamp assembly which will at least go some way towards making it simplerto secure an umbrella especially when used with items of furniture, orat least provide the public with a useful choice.

STATEMENTS OF THE INVENTION

Accordingly, in a first aspect, the invention may broadly be said toprovide a shaft clamp assembly comprising a bracket having a tubularmember adapted to receive a shaft, means for mounting the tubular memberto a structure, and clamping means, the clamping means being operable tosecure the shaft to the tubular member, and wherein the internal wall ofthe tubular member is provided with at least two shaft contact surfaces,their arrangement being such that a polygon of forces is generatedbetween the clamping means and the shaft contact surfaces to secure theshaft to the tubular member when the clamping means is operated.

Preferably the polygon of forces is a triangle of forces.

Preferably the tubular member comprises a tube having a substantiallytriangular cross section.

Preferably the radius of each apex of the substantially triangular crosssection is less than the radius of a shaft which is to be supported bythe shaft clamp assembly.

Preferably the clamping means includes at least one mechanism which isadapted to exert pressure on the shaft to push the shaft into contactwith at least two contact surfaces on the internal wall of the tubularmember.

Preferably the tubular member is provided with reinforcing members.

More preferably still the shaft contact surfaces are provided withreinforcing members.

Even more preferably the reinforcing members form part of the means formounting the tubular member to a structure.

The means to grip the shaft could include at least one lever and camarrangement to exert pressure onto the side of the shaft of an umbrella,to clamp it within the tube. However, preferably the clamping meansincludes at least one threaded shaft or rod, which is adapted to engagewith a mating thread associated with the tubular member.

Preferably the portion of the clamping means which contacts or grips theshaft incorporates a resilient member.

Preferably the thread associated with the tubular member further passesthrough one of the reinforcing members. Such an arrangement provides alonger and therefore stronger threaded portion.

The means for mounting the tubular member to a structure could includegusset pieces which are attachable to both the tubular member and to thestructure, or it could include a substantially rigid plate or platessecurely attached to the tubular member. However, preferably the meansfor mounting the tubular member to a structure comprises at least onestrut.

Preferably the or each strut is provided with means to secure one end ofeach strut to a support.

More preferably said means to secure one end of each strut to a supportis holes in a tab portion of the or each strut.

The shaft clamp assembly can be made from plastics material, however,preferably the shaft clamp assembly is primarily made from a metal ormetal alloy.

In a second aspect, the invention may broadly be said to consist in anitem of furniture, incorporating a shaft clamp assembly substantially asspecified herein.

Optionally an aperture in the item of furniture, need not necessarily besubstantially centrally located, within for example a table top. Withsuch a non-centred arrangement the item of furniture and umbrella can bere-orientated to achieve optimum protection for the users as the sunmoves or the direction of rain changes. Such an arrangement isparticularly useful if the umbrella is not a hinged umbrella. It will berealised that such a process will be far harder to achieve using some ofthe prior art arrangements, for example if a heavy base member were usedto support the umbrella.

In a third aspect, the invention may broadly be said to consist in anitem of furniture and an umbrella shaft and/or an umbrella incorporatinga shaft clamp assembly substantially as specified herein.

DESCRIPTION

The invention may also broadly be said to consist in the parts, elementsand features referred to or indicated in the specification of theapplication, individually or collectively, and any or all combinationsof any two or more of the parts, elements or features, and wherespecific integers are mentioned herein which have known equivalents,such equivalents are incorporated herein as if they were individuallyset forth.

One preferred form of the invention will now be described, by way ofexample only, with reference to the accompanying drawings in which,

FIG. 1 is a perspective view of a shaft clamp assembly,

FIG. 2 is a side elevation of the shaft clamp assembly,

FIGS. 3, 3 a and 3 b are respectively a cross sectional view through theclamping means of the shaft clamp assembly, a vector diagram showing atriangle of forces and a cross section of the end of the clamping means,

FIG. 4 is a perspective view of an item of furniture fitted with theshaft clamp assembly, complete with an umbrella installed,

FIG. 5 is a perspective view showing the use of the shaft clamp assemblyto support a sun umbrella on a solid foundation, and the use of a secondshaft clamp assembly to support a table top from the shaft of anumbrella, and

FIG. 6 is a perspective view showing the use of the shaft clamp assemblyto support a clothesline.

With reference to FIGS. 1 and 2, a shaft clamp assembly (10) is showncomprising at least a tubular member (11) of substantially uniformthickness, three struts (13), and a pair of clamping means (15). Thetubular member (11) is formed from a substantially triangular crosssectioned tube having three distinct flat side walls, and curved apexes.Each clamping means (15) comprises a threaded rod (17) the proximal endof which is secured to the centre of a knob (19). The threaded rod (17)engages with a mating thread which is formed in one of the flat sidewalls of the tubular member (11).

The arrangement of the struts (13) is such that an elongate portion ofeach strut (13) provides reinforcement for each respective flat sidewall of the tubular member (11). In addition, the mating thread extendsthrough this reinforcement portion of one of the struts (13) providing alonger and therefore stronger mating thread.

The struts (13) are used as a means for mounting the tubular member (11)to a structure. Clearly, while struts (13) have been used in thisexample, a variety of means for mounting the tubular member (11) to astructure could be used, for example, a flat plate which is welded tothe tubular member (11).

The struts (13) are formed from a flat bar section and are each attachedby welding to the exterior surface of a flat side wall of the tubularmember (11), the welded attachment extending along the majority of thelength of the tubular member (11). Such an attachment means that part ofeach strut (13) is able to reinforce the tubular member (11). The freeends of the struts (13) are further provided with tabs or feet (25), andeach of the feet (25) have five drilled holes (27) for the insertion ofbolts or screws when fastening the shaft clamp assembly (10) to astructure.

While the invention is not limited to the use of three struts (13), thisnumber of struts (13) is advantageous because the shaft clamp assembly(10) will not tend to wobble if fitted to a surface of a structure thatis not perfectly flat, for example when fitted to the under surface of atable where the table top has been manufactured from differentthicknesses of wood.

With reference to FIG. 3, the shaft (31) of an umbrella (31) can beinserted as shown into the tubular member (11) and secured using theclamping means (15). It is secured by turning one and preferably both ofthe knobs (19) and winding the threaded rods (17) towards the shaft (31)so that the ends (33) of the rods (17) push against the shaft (31)thereby clamping the shaft (31) between the rod (17) and a first and asecond shaft contact surface (35) and (37) of the tubular member (11).The first and second shaft contact surfaces (35) and (37) are theinternal faces of the two flat side walls of the tubular member (11)which do not contain the rod (17).

FIG. 3 a shows a triangle of forces which exists when the shaft (31) isclamped within the tubular member (11). Vector (17 a) represents theforce exerted by the threaded rod (17), vector (35 a) represents thereaction force exerted by the shaft contact surface (35) and vector (37a) represents the reaction force exerted by the shaft contact surface(37). The tubular member (11) in this example has a triangular crosssection which is similar to an equilateral triangle, that is, it hasthree flat side walls which are each arranged at sixty degrees to oneanother. For this reason, the triangle of forces, in which eachindividual force acts at ninety degrees to their respective flat sidewall, is also a triangle with vectors at sixty degrees to one another.

The triangular cross sectioned tubular member (11) as shown in FIG. 3has been found to produce a very effective clamp for the purpose ofsecuring a sun umbrella. The shaft (31) of the umbrella is held securelyalong the length of the tubular member (11) since the shaft (31) iseffectively wedged into a corner along the length of the triangulartubular member (11). Even if only a single clamping means (115) is used,the shaft (31) is constrained along two distinct lines, which are thelines of contact between the shaft (31) and the first and second contactsurfaces (35) and (37) of the interior of the tubular member (11). Theselines of constraint partially oppose one another.

A reaction force acts from each partially opposing line of constraint.These forces in combination with a third opposing force exerted by theclamping means (15) produce the triangle of forces which is exerted ontothe shaft (31). The triangle of forces act to largely eliminate anytendency for the shaft (31) to rock or move within the shaft clampassembly (10) when external loads are applied to the shaft (31). It isbelieved that this greatly improved constraint of the shaft (31) is notexperienced with prior art shaft clamp assemblies which are mostcommonly formed using a tubular member which has a circular crosssection. Where the tubular member has a circular cross section, there istypically only a single line of contact between a shaft and the tubularmember, and for this reason the shaft is able to rock or move within thetubular member with relative ease. And since the shafts of sun umbrellasexperience relative large forces due to the effects of wind loads on thecanopy of the umbrella, the restraint of the shaft within a shaft clampassembly is important.

Whilst the shaft clamp assembly (10) will work well with only oneclamping means (15), there is an advantage in providing two or moreclamping means (15). If two clamping means (15) are used, one can bepositioned towards each end of the tubular member (11) to furtherimprove the ability of the shaft clamp assembly (10) to firmly attach toa shaft, with very little possibility of the shaft rocking or moving inany axis within the shaft clamp assembly (10).

In this example, the clamping means (15) is in the form of a threadedrod (17) and a knob (19), but clearly many other types of clamping meanscould be used, for example a lever and cam arrangement. However, theclamping means (15) used in the example is advantageous in that it issimple, and it can be used to clamp against shafts of varying diameterswithout the need for any adjustment of the clamping means.

FIG. 3 b shows an optional arrangement of the distal or free end (33) ofthe threaded rod (17). In this option, a concentric hole is formed inthe free end (33) of the threaded rod (17), and a complimentary mating“T” shaped plug (34) which is made of a suitable resilient material isinserted into the hole. The plug (34) covers the free end (33) and helpsto minimise damage to the surface of a constrained shaft (31), which mayotherwise be caused by the free end (33) of the threaded rod (17) whenthe shaft clamp assembly (10) is in use. In this case, the plug (34) ismade from a plastics material.

With reference to FIG. 4, a shaft clamp assembly (10) is shown fitted tothe underside surface of an outdoor table (39). The shaft (31) of theumbrella (41) passes through an aperture (43) substantially centrallylocated within the table top (45) and the shaft (31) is rigidly securedin the shaft clamp assembly (10). With this arrangement no additionalbase is required for the umbrella, and neither is it necessary to engagethe bottom of the shaft (31) with the ground.

The assembly of the table (39), shaft clamp assembly (10) and umbrella(41) has improved resistance to light winds, can easily be moved as anassembly, and provides good leg and foot room under the table. Asdiscussed earlier, if the aperture (43) in the table top, and the shaftclamp assembly (10) were situated offset from the centre of the table(39), the table (39) could be orientated to give the best shelter,depending on the angle of the sun, or the direction of the rain.

With reference to FIGS. 5 and 6, two additional methods of use of theshaft clamp assembly (10) are shown.

In FIG. 5 a first shaft clamp assembly (10) is used to secure the shaft(10) of an umbrella (41) to a support (60). The support (60) can takemany forms, for example a plinth, a concrete foundation, or a handrail,etc. A second shaft clamp assembly (10) is used to secure a table top orplatform (47) to the shaft (31) of an umbrella. The table top orplatform (47) can be mounted at any height above the ground to form atable for a range of purposes, for example a table to lean on, a tableto sit at, or a drinks table to use whilst seated on the ground.

While this example shows a table top (47) secured to a shaft (31), manyitems such as spot lights, speakers etc, could be secured to a shaftusing the shaft clamp assembly (10).

In FIG. 6 a shaft clamp assembly (10) is used to attach a shaft (49) ofa clothesline (51) to a support (not shown).

The examples shown in FIGS. 4, 5 and 6 show the versatility of the shaftclamp assembly (10) as specified herein. There will also be a number ofother uses for it, for example, supporting an advertisement banner,supporting a road sign, or the like.

ADVANTAGES

Thus it can be seen that at least the preferred form of the inventionprovides a shaft clamp assembly (10) that is capable of securing theshaft of an umbrella (41) to an item of furniture (39), such that theumbrella (41) has good stability, the item of furniture (39) can bemoved with relative ease. Similarly it is easier to stow seats under atable (39) incorporating the invention, as the seats would no longerconflict with a large conventional umbrella base block.

And, safety can be enhanced in that the chance of an umbrella (41) beingblown out of a table (39), or being blown over, in the wind is likely tobe reduced. Stability of the table (39) can also be improved since theclamped umbrella shaft (41) can act as an extra leg for the table.

The shaft clamp assembly (10) is also very versatile and can be used tosupport the shafts of a range of items, such as clotheslines, banners,signposts, and it can equally be used to secure an item to a shaft, suchas a table top, a light, etc.

1. A shaft clamp assembly comprising a bracket having a tubular memberadapted to receive a shaft, means for mounting the tubular member to astructure, and clamping means, the clamping means being operable tosecure the shaft to the tubular member, and wherein the internal wall ofthe tubular member is provided with at least two shaft contact surfaces,their arrangement being such that a polygon of forces is generatedbetween the clamping means and the shaft contact surfaces to secure theshaft to the tubular member when the clamping means is operated.
 2. Ashaft clamp assembly as claimed in claim 1, wherein the polygon offorces is a triangle of forces.
 3. A shaft clamp assembly as claimed inclaim 1, wherein the tubular member comprises a tube having asubstantially triangular cross section.
 4. A shaft clamp assembly asclaimed in claim 3, wherein the radius of each apex of the substantiallytriangular cross section is less than the radius of a shaft which is tobe supported by the shaft clamp assembly.
 5. A shaft clamp assembly asclaimed in claim 1, wherein the clamping means includes at least onemechanism which is adapted to exert pressure on the shaft to push theshaft into contact with at least two contact surfaces on the internalwall of the tubular member.
 6. A shaft clamp assembly as claimed inclaim 1, wherein the tubular member is provided with reinforcingmembers.
 7. A shaft clamp assembly as claimed in claim 6, wherein theshaft contact surfaces are provided with reinforcing members.
 8. A shaftclamp assembly as claimed in claim 6, wherein the reinforcing membersform part of the means for mounting the tubular member to a structure.9. A shaft clamp assembly as claimed in claim 1, wherein the clampingmeans includes at least one threaded shaft or rod, which is adapted toengage with a mating thread associated with the tubular member.
 10. Ashaft clamp assembly as claimed in claim 9, wherein the threadassociated with the tubular member further passes through one of thereinforcing members.
 11. An item of furniture, incorporating the shaftclamp assembly of claim
 1. 12. A shaft clamp assembly as claimed inclaim 2, wherein the tubular member comprises a tube having asubstantially triangular cross section.
 13. A shaft clamp assembly asclaimed in claim 2, wherein the clamping means includes at least onemechanism which is adapted to exert pressure on the shaft to push theshaft into contact with at least two contact surfaces on the internalwall of the tubular member.
 14. A shaft clamp assembly as claimed inclaim 3, wherein the clamping means includes at least one mechanismwhich is adapted to exert pressure on the shaft to push the shaft intocontact with at least two contact surfaces on the internal wall of thetubular member.
 15. A shaft clamp assembly as claimed in claim 4,wherein the clamping means includes at least one mechanism which isadapted to exert pressure on the shaft to push the shaft into contactwith at least two contact surfaces on the internal wall of the tubularmember.
 16. A shaft clamp assembly as claimed in claim 2, wherein thetubular member is provided with reinforcing members.
 17. A shaft clampassembly as claimed in claim 3, wherein the tubular member is providedwith reinforcing members.
 18. A shaft clamp assembly as claimed in claim4, wherein the tubular member is provided with reinforcing members. 19.A shaft clamp assembly as claimed in claim 5, wherein the tubular memberis provided with reinforcing members.
 20. A shaft clamp assembly asclaimed in claim 2, wherein the clamping means includes at least onethreaded shaft or rod, which is adapted to engage with a mating threadassociated with the tubular member.